Database Systems
A database management system (DBMS) manages a database. A DBMS may comprise one or more database servers. A database comprises database data and a database dictionary that are stored on a persistent memory mechanism, such as a set of hard disks. Database data may be stored in one or more data containers. Each container contains records. The data within each record is organized into one or more fields. In relational DBMSs, the data containers are referred to as tables, the records are referred to as rows, and the fields are referred to as columns. In object-oriented databases, the data containers are referred to as object classes, the records are referred to as objects, and the fields are referred to as attributes. Other database architectures may use other terminology.
Users interact with a database server of a DBMS by submitting to the database server commands that cause the database server to perform operations on data stored in a database. A user may be one or more applications running on a client computer that interact with a database server. Multiple users may also be referred to herein collectively as a user.
A database command may be in the form of a database statement that conforms to a database language. A database language for expressing the database commands is the Structured Query Language (SQL). There are many different versions of SQL, some versions are standard and some proprietary, and there are a variety of extensions. Data definition language (“DDL”) commands are issued to a database server to create or configure database objects, such as tables, views, or complex data types. SQL/XML is a common extension of SQL used when manipulating XML data in an object-relational database.
A multi-node database management system is made up of interconnected nodes that share access to the same database. Typically, the nodes are interconnected via a network and share access, in varying degrees, to shared storage, e.g. shared access to a set of disk drives and data blocks stored thereon. The nodes in a multi-node database system may be in the form of a group of computers (e.g. work stations, personal computers) that are interconnected via a network. Alternately, the nodes may be the nodes of a grid, which is composed of nodes in the form of server blades interconnected with other server blades on a rack.
Each node in a multi-node database system hosts a database server. A server, such as a database server, is a combination of integrated software components and an allocation of computational resources, such as memory, a node, and processes on the node for executing the integrated software components on a processor, the combination of the software and computational resources being dedicated to performing a particular function on behalf of one or more clients.
Resources from multiple nodes in a multi-node database system can be allocated to running a particular database server's software. Each combination of the software and allocation of resources from a node is a server that is referred to herein as a “server instance” or “instance”. A database server may comprise multiple database instances, some or all of which are running on separate computers, including separate server blades.
Database Consolidation
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.
Database consolidation involves distributing and sharing computer resources of a hardware platform among multiple databases. Important objectives of database consolidation include isolation, transportability, and fast provisioning. Isolation is the ability to limit an application's access to the appropriate database; an application is permitted access to a database while other applications are prevented access.
Users, Privileges, and Roles
For security purposes, DBMSs often maintain a list of valid database users. To access a database, a user typically connects to a database server instance and provides a username and password. The database server then checks the user name and password against the list of valid users defined in the database to determine whether to grant the user access.
In some cases, DBMSs allow the resources available to each user of the database to be customized. The right to access a particular resource of the database will be referred to as a privilege. For example, a privilege may represent the right to execute a particular type of database command or the right to access a particular database object.
For convenience, some DBMSs allow multiple privileges to be bundled into a package referred to as a role. Thus, when a user is granted a role, the user obtains all the privileges associated with the role. For example, the database may define a role associated with high ranking users that includes nearly all available privileges, such as the ability to assign privileges to other users, create and modify database objects, etc. In addition, the database may define a role associated with low-ranking users, which may possess some privileges, such as the ability to connect with the database and perform queries, but lack other privileges such as the right to modify database objects.
Often, DBMSs are installed by default with an administrator that possesses global access to the databases resources. The administrator then creates the other users and assigns roles and privileges.